Advanced consumer electronics such as miniature radios and wristwatch cellular phones pose severe limitations on the size and cost of frequency selective units contained therein. MEMS (micro-electro-mechanical systems) resonators are receiving increased attention as building blocks for integrated filters and frequency references to replace bulky, off-chip ceramic and SAW (surface acoustic wave) devices, among others. Small size, low power consumption and ease of integration with microelectronic circuits constitute the major advantages of MEMS resonators.
Several all-silicon resonators with capacitive transduction mechanisms are known, revealing high mechanical quality factors (Q) and optimal performance in the IF (intermediate frequency) and VHF (very high frequency) range. However to reduce the motional resistance of such capacitive resonators for higher frequency applications, gap spacing on the order of nanometer dimensions are often required, which can complicate the fabrication process for these devices.
Piezoelectric Film Bulk Acoustic Resonators (FBAR), characterized by a lower motional resistance than their capacitive counterparts, have proven to be suitable for UHF (Ultra-high frequency) applications. However, FBAR resonators generally have low quality factors and no electrostatic fine-tuning capabilities. Further, fabrication methods for these devices are limited practically in their ability to create thick and/or uniform mechanical layers due in part to the long processing times associated with fabrication of thick substrates.
Thus, a need exists in the industry to address the aforementioned and/or other deficiencies and/or inadequacies.